Selenium and amino acid composition of selenoprotein P, the major selenoprotein in rat serum

• Published in: The Journal of biological chemistry 1990-10, Vol.265 (29), p.17899-17905
• Main Authors: Read, R, Bellew, T, Yang, J G, Hill, K E, Palmer, I S, Burk, R F
• Format: Article
• Language: English
• Subjects: Amino Acids - analysis; Animals; Cyanogen Bromide; Electrophoresis, Polyacrylamide Gel; Glycoproteins - blood; Glycoproteins - chemistry; Glycoproteins - isolation & purification; Male; Molecular Weight; Peptide Fragments - isolation & purification; Proteins - chemistry; Proteins - isolation & purification; Rats; Rats, Inbred Strains; selenium; Selenium - blood; Selenium - chemistry; Selenium - isolation & purification; Selenoprotein P; Selenoproteins; Trypsin
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)38248-6

Selenoprotein P is the second plasma selenoprotein to be purified. It is a glycoprotein and has been shown to be distinct from plasma glutathione peroxidase. This study characterizes selenoprotein P further. Deglycosylation of the protein shifts its migration on sodium dodecyl sulfate-polyacrylamide gel electrophoresis from Mr 57,000 to Mr 43,000, indicating it has a substantial carbohydrate component. Measurement of selenium indicates a selenium content of 7.5 +/- 1.0 atoms/molecule based on a polypeptide weight of 43,000. Amino acid analysis accounts for all the selenium as selenocysteine. The protein is also rich in cysteine (17 residues) and histidine (23 residues). Fragmentation of selenoprotein P by trypsin and by cyanogen bromide produces peptides with varying selenium content. This indicates that selenium-rich regions of the protein exist. The concentration of selenoprotein P determined by radioimmunoassay in serum from control rats is 26.3 +/- 4.5 micrograms/ml and in serum from selenium-deficient rats it is 2.7 +/- 0.8 micrograms/ml. Depletion of selenoprotein P from control serum using an immunoaffinity column indicates that over 60% of serum selenium in the rat is contained in this protein. These results demonstrate that selenoprotein P is the major form of selenium in rat serum. It is the first selenoprotein described which has more than one selenium atom/polypeptide chain.